newer versions of devel headers expose CLONE flags only with _GNU_SOURCE
defined


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13035 a5019735-40e9-0310-863c-91ae7b9d1cf9
diff --git a/none/tests/s390x/test_clone.c b/none/tests/s390x/test_clone.c
index 7f69c89..60d515a 100644
--- a/none/tests/s390x/test_clone.c
+++ b/none/tests/s390x/test_clone.c
@@ -1,3 +1,4 @@
+#define _GNU_SOURCE
 #include <sys/syscall.h>
 #include <linux/wait.h>
 #include <sched.h>